1. Field of the Invention
The present invention relates to systems and methods for protecting vehicle occupants from injury. More specifically, the present invention relates to a dual stage biaxial inflator that injects multiple gas flows along a substantially identical axis in opposing directions into an airbag system, such as an inflatable curtain, and that provides an extended gas delivery period.
2. Description of Related Art
The inclusion of inflatable safety restraint devices, or airbags, is now a legal requirement for many new vehicles. In addition to this, inflatable airbags enjoy widespread acceptance for use in motor vehicles and are credited with preventing numerous deaths and injuries. Some studies estimate that the use of frontally-placed airbags reduces the number of fatalities in head-on collisions by 25% among drivers using seat belts and by more than 30% among unbelted drivers. Other research suggests that in a frontal collision, the combination of a seat belt and an airbag can reduce serious chest injuries by 65% and serious head injuries by up to 75%. These numbers and the thousands of prevented injuries they represent demonstrate the life-saving potential of airbags and the need to encourage their use, production, and development.
As a result in part of benefits such as those described above, automakers are now required to install airbags in most new vehicles bound for sale in the United States. Many automobile manufacturers have turned this requirement of implementation of airbag technology into a marketing tool. Enticed by the promise of added safety, vehicle purchasers frequently seek out vehicles with sophisticated airbag systems.
Airbags are typically installed in the steering wheel and in the dashboard on the passenger side of a car. In the event of an accident, an accelerometer situated within the vehicle measures the abnormal deceleration caused by the accident and triggers the expulsion of rapidly expanding gases from an inflator into each of the airbags. The expanding gases rapidly fill the airbags, which immediately inflate in front of the driver and passenger to protect them from impact against the windshield, dashboard, or steering wheel. Thus used, vehicular airbags have saved countless human lives.
As a result of the success of front-installed airbags, other airbags designed to protect occupants in other types of vehicular collisions have been developed. Side impact airbags, often in the form of inflatable curtains, were one such airbag developed in response to the need for protection from impacts in a lateral direction, or against the side of the vehicle. Such curtains are placed along the side of a vehicle in places such as the ceiling or roof rails. An inflatable curtain may be composed of one or more separately inflated cushions that protect individual passengers in different positions within the vehicle.
Side impact cushions are often designed to unfold or unroll downward from their installation site to inflate beside a vehicle occupant to keep the vehicle occupant from hitting the door or window during a lateral impact event. Since the vehicle occupant may be leaning forward, reclined in the seat, or at any position between, such cushions are often made somewhat long to ensure that even such an xe2x80x9cout-of-positionxe2x80x9d occupant hits the cushion.
In some installations, multiple cushions may be fed by a single inflator as a result of space constraints or other considerations. The inflator may be placed at either end of a cushion. In situations where multiple cushions are fed by a single inflator positioned either fore or aft of the cushions, an especially long gas flow path exists between the inflator and the cushion furthest from the inflator. This long gas flow path may reduce the speed of the gas flow, thus resulting in delayed inflation of the furthest cushions. Furthermore, the outermost extents of an inflatable curtain in such an installation may receive insufficient inflation gas pressure to inflate the curtain to the optimal protective pressure.
Even in somewhat shorter cushions, rapid and even inflation can be difficult to achieve with known inflator designs. Many existing inflators eject inflation gases outward radially. As a result of this, the inflation gases are not propelled along the length of the cushion with sufficient force to reach its outer edges, but are instead largely directed into the cushion near the inflator. The outer regions of the cushion are thus inflated later than those closest to the inflator.
Additionally, some inflatable curtain systems are somewhat expensive due to the need for multiple inflators, attachment mechanisms, and the like. Many inflatable curtain systems require the use of a xe2x80x9cgas guide,xe2x80x9d or conduit that conveys gas from the inflator to the inflatable curtain. Some known inflators require the use of multiple initiators that add to the manufacturing expense and timing requirements of the inflator.
In addition to this, in collisions which result in vehicle rollovers, the time period during which a vehicle occupant may be injured by striking a lateral side of the vehicle is often much longer than in a conventional collision. As a result of this, it would be beneficial to the occupants for the airbags to remain inflated during that period in order to protect them from injury. Conventional inflators, however, are largely incapable of providing such a long inflation.
Further, in some collisions, it would be beneficial for an airbag inflator to be xe2x80x9csmart,xe2x80x9d or capable of providing different amounts of gas to an airbag to give it different hardnesses in response to different collisions. Most currently known airbags are capable of providing a single inflation pressure. Similarly, some benefit would be gained from an inflator that is capable of providing a secondary flow of inflation gas at a slight delay from a primary flow of inflation gas in order to either maintain inflation of an airbag or reinflate an airbag.
In addition to the above, it should be noted that many airbag inflators currently used in vehicles produce thrust upon activation. As a result of this thrust, complex attachment mechanisms must often be used to affix the inflators to the vehicle in which they are installed to ensure that the inflators do not dislodge themselves during deployment. Inflators expel gas with such force that if they were to be dislodged from their placement, they could endanger vehicle occupants. Such additional attachment parts often increase the cost of the inflatable curtain system, as well as the time and expense required to install the inflatable curtain system in a vehicle. Complicated attachment mechanisms may also pose engineering problems which are time-consuming and expensive to resolve.
Accordingly, a need exists for an inflator and related methods that remedy problems found in the prior art. Such an inflator should preferably provide relatively even and rapid inflation of an associated inflatable curtain, preferably without requiring multiple inflators for a single curtain, and preferably while producing little or no thrust. Such an inflator should also preferably be simple and inexpensive to manufacture and install.
The apparatus of the present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available inflators. Thus, it is an overall objective of the present invention to provide a dual stage biaxial inflator and related systems and methods that provide rapid, even inflation of an airbag such as an inflatable curtain with a minimum of manufacturing and installation cost.
To achieve the foregoing objective, and in accordance with the invention as embodied and broadly described herein in the preferred embodiment, a dual stage biaxial inflator having a primary gas chamber, a flow restrictor, and a secondary gas chamber is disclosed. The inflator may comprise a primary gas chamber with a first end disposed within a first inlet port of the inflatable curtain and a second end disposed within a second inlet port of the inflatable curtain. The primary gas chamber may comprise one unitary body. The first and second inlet ports may be tightly affixed to the gas chamber such that gas is unable to escape from the inflatable curtain between the inlet ports and the gas chamber. The secondary gas chamber may be in gaseous communication with the primary gas chamber through the flow restrictor, which is positioned between the primary gas chamber and the secondary gas chamber. The inflator may additionally include an initiator in communication with at least one of the gas chambers for initiating a flow of gas through the exit orifices.
The primary gas chamber may have a first exit orifice positioned at a first end and a second exit orifice positioned at a second end. Each exit orifice may have a sealed configuration that does not permit gas flow, and an open configuration, in which inflation gases flow relatively freely out of the gas chamber through the exit orifice. Each exit orifice may take the form of an interior cap with an opening covered by a burst disc; the burst discs may be removed from the openings via a pressure shock induced by combustion within the gas chamber. Burst disc retention members may be disposed outside the openings to capture the burst discs and ensure that they do not damage the inflatable curtains.
Each exit orifice may also have an ejection nozzle that controls the flow of inflation gas out of the exit orifice. The ejection nozzles may be aligned with the longitudinal axis of the inflator so that inflation gases are ejected along the longitudinal axis. The ejection nozzles of the first and second exit orifices may be directed opposite to each other so that thrust from the first exit orifice substantially negates the thrust from the second exit orifice, and vice versa. As a result, the inflation gases are ejected in directions substantially opposite each other.
The secondary gas chamber is positioned in gaseous communication with the primary gas chamber through the flow restrictor. The flow restrictor has a flow restrictor orifice that in some inflators has a sealed configuration and an open configuration. In those inflators where the flow restrictor has only an open configuration, inflation charges placed within the primary and secondary gas chambers may be allowed to mingle. In those inflators that include a flow restrictor having a sealed configuration, the seal may be formed by a frangible seal such as a burst disc, scored surface, or compression seal. Inflators that have burst discs may also have burst disc retention members to retain the burst disc after initiation of the inflator.
The flow restrictor that connects the primary and secondary gas chambers may simply include a restricted flow channel. This channel is defined using methods known in the art to be sufficiently narrow to meter the flow of an inflation gas produced by the inflation charge of the secondary gas chamber such that the flow of gas is lengthened out to a predetermined duration. This duration could be selected by tuning the diameter of a restricted flow channel.
The inflator may have an initiator disposed within the assembly that activates a gas-producing material to create first and second primary gas flows through the first and second exit orifices of the primary gas chamber, respectively. The initiator assembly may be positioned within the primary gas chamber, the secondary gas chamber, or both gas chambers.
The inflator of the invention may also include a gas generant, or gas-producing material in the form of a solid, liquid, gas, or liquid/gas mixture that has been cryogenically inserted into the gas chambers in solid form. The initiator of the inflator is positioned to heat the liquid/gas mixture, thus causing gas generation and initiating the rise in pressure or pressure shock. This increase in pressure or pressure shock may remove the burst discs from the openings or otherwise place the exit orifices into their open configurations. This change in configuration allows the flows of gas from the exit orifices to begin.
The inflator of the invention is capable of providing primary and secondary gas flows to inflate and then maintain the inflation of an airbag or inflatable curtain. The primary gas flow is provided primarily by the inflation charge housed within the primary gas chamber or chambers. This primary gas flow is split into a first and a second primary gas flow, proceeding from the first and second exit orifices, respectively, of the primary chamber. This primary gas flow is largely responsible for the initial inflation of the airbag or inflatable curtain. The secondary gas flow is produced primarily from the inflation charge housed within the secondary gas chamber or chambers. This secondary flow of gas is triggered either passively as the pressure of the primary gas chamber decreases, or actively by a pressure gradient which could be created by an initiator associated with the secondary gas chamber. This secondary flow of gas proceeds out of the secondary gas chamber into the primary gas chamber, and is then split into first and second secondary gas flows which are ejected from the first and second exit orifices, respectively. This secondary flow of gas may be used to maintain the inflation of the airbag or inflatable curtain, or, in some cases, to reinflate it. In addition, in so-called xe2x80x9csmartxe2x80x9d airbag systems, the secondary flow of gas may be initiated in response to collisions of a particular nature or severity, or initiated only when the vehicle occupant to be protected by the inflatable cushion is of a certain size or weight.
According to one alternative, the inflator may comprise multiple secondary and/or primary gas chambers in order to provide a controllable, customizable flow of gas. The gas chambers may be vessels having a generally tubular shape. As discussed briefly above, these chambers may have frangible seals such as the openings and burst discs discussed above, or scored, or notched, surfaces that open when the pressure within the gas chamber exceeds the strength of the scored regions. The scored surface may open to form a suitable exit nozzle. Additionally, the frangible seal may be a compression closure, such as a crimped opening. The crimped opening may have two lips pressed flat together and attached through a method such as welding. As with the scored region, the crimped opening opens in response to a pressure shock and/or increase within the gas chamber, and may be configured to form a suitable exit nozzle upon opening. In each of these alternatives, some physical puncture mechanism may be used to assure that the frangible seal opens when activated by the initiator.
As with the previous inflator, a gas-producing material such as a compressed gas and liquid mixture may be thermally activated by an initiator to provide first and second primary and secondary gas flows through the first and second exit orifices, respectively. In order to ensure that the frangible seals over both exit orifices burst completely and simultaneously, tight tolerancing of the burst discs, scored surfaces, or compression seals may be implemented.
According to another embodiment of the invention, the dual stage biaxial inflator for a vehicular airbag system may include a first primary gas chamber having a first longitudinal axis and a first exit orifice configured to provide a first primary gas flow oriented substantially along the longitudinal axis, the first exit orifice having an open and a closed configuration. Additionally, the inflator may include a second primary gas chamber having a second longitudinal axis and a second exit orifice configured to provide a second primary gas flow oriented substantially along the longitudinal axis; the second exit orifice having an open and a closed configuration. The inflator additionally has a secondary gas chamber in gaseous communication with said first and second primary gas chambers configured to provide a secondary gas flow and a flow restrictor positioned between each primary gas chamber and the secondary gas chamber. The inflator also includes an initiator in communication with the interior of one of said gas chambers, the initiator being configured to selectively initiate a flow of gas through the exit orifice.
In this inflator, the secondary gas chamber may be located between the first and second primary gas chambers. The first and second exit orifices of the first and second primary gas chambers may be configured to provide first and second primary gas flows which have substantially equivalent amounts of gas. Further, the first and second exit orifices may be configured to provide first and second primary gas flows which have different amounts of gas. In addition, the inflator may be constructed so that the first longitudinal axis and the second longitudinal axis are equivalent. In inflators where the first and second primary gas flows are identical, and where the first and second longitudinal axes are identical, a substantially zero-thrust inflator may be provided. Such a zero-thrust inflator may be provided under the first embodiment, as well. In this inflator, each primary gas chamber may have its own initiator. Additionally, the secondary gas chamber may have its own initiator.
Through the use of the inflators of the present invention, cost savings may be obtained through the elimination of gas guides, complex attachment features, and redundant inflators and initiators. Additionally, more rapid and even inflation of the inflatable curtains may be obtained, and sustained inflation of the inflatable curtains may be achieved. As a result, the availability and effectiveness of vehicular airbag systems may be enhanced.
These and other objects, features, and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.